1. Field of the Invention
The present invention relates to an over drive control device of a direct current series motor and more particularly to the over drive control apparatus to stably control the speed of the over drive.
2. Description of the Prior Art
The over drive apparatus increases the number of rotations of the transmission axle to more than the base speed of the motor. This device is generally used in industrial electric vehicles to which a light load is applied for actuating the vehicles above the base speed to control the magnetic flux by adjusting the current amount in the field winding.
FIGS. 1 and 2 show a conventional over drive control apparatus.
The over drive apparatus shown in FIG. 1 comprises a field winding 3 for rotating the armature winding 2 by generating the magnetic field using power from the battery 1, forward and backward connector 4 for controlling the direction of rotations of the armature 2 by controlling the direction of the current in the field winding 3, chopper transistor 5 for switching the power from battery 1 either to the armature winding 2 or to the field winding 3, bypass contactor 6 for preventing instanteneous over-voltage in the chopper transistor 5 during conversion from normal state to over drive state, over drive transistor 7 for switching the power supply from the battery to the field winding 3, and a microcomputer 8 for performing over drive function by controlling the current amount to the field winding 3 in response to the control of the on-off operation of the chopper transistor 4 and by controlling the current flowing in the field winding 3 in response to the control of on-off operation of the over drive transistor 7.
In FIG. 2, the over drive transistor 7 is replaced with the over drive contactor 9 to select either the normal state or over drive state.
However, since the conventional over drive control apparatus as shown in FIG. 1 uses the over drive transistor 7 which is on-off controlled by the microcomputer 8 so as to control the over drive state, the driving control circuit is additionally required to drive the over drive transistor 7, thereby increasing the manufacturing cost.
Further, the armature winding 2 and field winding 3 is placed on top of the chopper transistor 5 and power from the battery 1 is directed through both the armature winding 2 and field winding 3 to the chopper transistor 5, by which the current amount in the chopper transistor 5 has become unstable. Accordingly, as the driving characteristic of the chopper transistor 5 become unstable, it has another problem that the control of the system becomes unreliable.
The over drive apparatus of FIG. 2 shows the use of the over drive contactor 9 instead of the over drive transistor 7 of FIG. 1. This reduced the manufacturing cost, however, the location of the armature winding 2 and the field winding 3 in front of the chopper transistor 5 cause the same problem in that the control of the system becomes unreliable.